1. Field of the Invention
This invention relates to an ink jet printing system and more particularly to a thermal drop-on-demand ink jet printing system.
2. Description of the Prior Art
A thermal drop-on-demand ink jet printing system is known in which a heater is selectively energized to form a "bubble" in the adjacent ink. The rapid growth of the bubble causes an ink drop to be ejected from a nearby nozzle. Printing is accomplished by energizing the heater each time a drop is required at that nozzle position to produce the desired printed image.
One thermal drop-on-demand ink jet printing system is described in U.S. Pat. No. 4,520,373 to Ayata et al. The print head in the Ayata et al system utilizes a heater substrate in which the ink drops are ejected in a direction parallel to thc plane of the heater element. The Ayata system comprises a plurality of chips each having the heater elements, the conductor elements and a control transistor array all on one side of a chip, with a heat sink on the other side of the chip.
Another thermal drop-on-demand ink jet printing system is described in U.S. Pat. No. 4,601,777 to Hawkins et al in which the ink drops are ejected in a direction normal to the plane of the heater element. The Hawkins printer comprises a chip which includes an array of heating elements and addressing electrodes, a silicon substrate into which an array of grooves is anisotropically etched, and a fixedly mounted electrode board. The silicon substrate is bonded to the heater chip so that one end of the grooves is aligned to serve as the nozzle and a second recess serves as the ink manifold. Electrical leads from the heater chip are wire bonded to corresponding conductor pads on the electrode board.
The prior art thermal drop-on-demand ink jet printing systems are unsuitable for a high resolution array having a large number of channels since their design does not permit the required electrical connections to be made in a compactly designed print head. Neither of the two designs disclose a heater chip with through hole electrical connections to solder pads on the opposite side of the heater chip.